Medical screw

Abstract

The outer periphery of a head section (11e) of a medical screw (11) is provided with an inverse external screw thread (11h) that is formed in the opposite screw direction from that of a screw thread (11b) provided to a tip section (11a). An inverse internal screw thread (14a) provided to the leading end of a rod-shaped body constituting an extraction jig (14) is rotated in the opposite direction from the screw direction of the screw thread (11b) so as to be screwed onto the inverse external screw thread (11h) and thereby integrate the screw (11) and the extraction jig (14). The screw (11) is gently extracted from the bone fracture site (D) and is removed from the body by rotating the extraction jig in the reverse direction from the insertion direction of the screw (11).

The invention claimed is: 
     
       1. A medical screw formed of a metallic material for joining a fracture site comprising:
 a screw thread portion formed on an outer surface of a distal end portion; and 
 an external thread portion formed on an outer periphery of a head portion of a rear end portion, 
 wherein a top surface of the head portion bulges in an arcuate shape, and 
 wherein the external thread portion is screwed with a withdrawal operating jig and formed in a reverse direction to a direction of a thread of the screw thread portion. 
 
     
     
       2. The medical screw according to  claim 1 , wherein a through hole for insertion of a guide pin is formed from the distal end portion to the head portion along a center axis. 
     
     
       3. The medical screw according to  claim 1 , wherein the entire length is 30 to 60 mm. 
     
     
       4. The medical screw according to  claim 2 , wherein the entire length is 30 to 60 mm. 
     
     
       5. The medical screw according to  claim 1 , wherein a plurality of groove portions are formed on an outer periphery of the head portion in a direction orthogonal to the circumferential direction. 
     
     
       6. The medical screw according to  claim 2 , wherein a plurality of groove portions are formed on an outer periphery of the head portion in a direction orthogonal to the circumferential direction. 
     
     
       7. The medical screw according to  claim 1 , wherein the screw thread portion is a right-handed thread, and the external thread portion is a left-handed thread. 
     
     
       8. The medical screw according to  claim 2 , wherein the screw thread portion is a right-handed thread, and the external thread portion is a left-handed thread.